Epoxidation process and catalyst therefore

ABSTRACT

A crystalline molecular sieve having a framework structure isomorphous with zeolite beta and containing Si and Ti, but essentially no framework Al, usefully catalyzes olefin epoxidation wherein hydrogen peroxide is the oxidant.

FIELD OF THE INVENTION

This invention relates to methods of selectively oxidizing olefins so asto obtain products containing epoxide functional groups. In particular,the invention pertains to processes whereby a hydrogen peroxide sourceis reacted with an ethylenically unsaturated substrate in the presenceof a relatively large pore crystalline titanium-containing molecularsieve catalyst to yield an epoxide. The catalyst is characterized by aframework structure isomorphous to zeolite beta comprised of silica andtitanium, but essentially free of framework aluminum.

BACKGROUND OF THE INVENTION

Many different methods for the preparation of epoxides have beendeveloped. One such method involves the epoxidation of an olefin in aliquid phase reaction using an organic hydroperoxide as the oxidizingagent and certain solubilized transition metal compounds as catalyst.Although this approach is practiced commercially and generally provideshigh selectivity to epoxide, it has at least two characteristics whichtend to limit process flexibility and increase production costs. The useof an organic hydroperoxide results in the generation of a co-productalcohol derived from the reacted hydroperoxide during epoxidation;approximately 1 equivalent of the co-product is obtained for eachequivalent of epoxide. If no market exists for the alcohol, theco-product must either be further reacted (incurring additionalprocessing costs) so as to convert it back to the hydroperoxide oxidantor to another compound for which a commercial demand exists. Recovery ofthe soluble metallic catalyst used in such a process for reuse insubsequent runs is also problematic. It would therefore be highlydesirable to develop an insoluble (heterogeneous) epoxidation catalystwhich has high activity and selectivity when utilized with an oxidantsuch as hydrogen peroxide which does not form an organic co-product.Such a catalyst would ideally be readily recoverable in active form froman epoxidation reaction mixture by filtration or similar separationtechniques or be capable of being utilized in the form of a fixed bed orthe like.

Workers at the Universidad Politecnica de Valencia have recentlyreported the synthesis of a titanium silicoaluminate isomorphous tozeolite beta (see Camblor et al., J. Chem. Soc., Chem. Commun. pp.589-590 (1992), Camblor et al., Zeolites 13, pp. 82-87 (1993) and ES2037596 (published Jun. 16, 1993)). Such aluminum-containing materialswere found to catalyze the oxidation of alkanes to alcohols, ketones,and the like using hydrogen peroxide as the oxidant. This type oftitanium silicoaluminate in unmodified (fully protonated) form is a poorcatalyst for the production of epoxides from olefins, however.

SUMMARY OF THE INVENTION

We have now made the unexpected discovery that a crystallinetitanium-containing molecular sieve characterized by a frameworkstructure isomorphous to zeolite beta and comprised of Si and Ti atoms,but essentially free of framework aluminum, selectively catalyzes theepoxidation of olefins using hydrogen peroxide or a hydrogen peroxideprecursor.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an X-ray powder diffraction pattern of the titanium-containingmolecular sieve prepared using the procedure of Example 1.

DETAILED DESCRIPTION OF THE INVENTION

In the process of this invention, an olefin is contacted with hydrogenperoxide or a substance capable of producing hydrogen peroxide under thereaction conditions in the presence of a catalytically effective amountof a tietanium-containing molecular sieve. The titanium-containingmolecular sieve suitable for use is characterized by a frameworkstructure isomorphous to zeolite beta. Si and Ti atoms are present inthe framework structure (typically, in the form of oxides). Theframework of the molecular sieve is essentially free of aluminum (Al),however, since the presence of significant amounts of Al has been foundto detrimentally affect the performance of said molecular sieve as anepoxidation catalyst unless the protons associated with aluminum aresubstituted with ammonium, alkali metal, or alkaline earth cations. Inthis context, "essentially free" means that the framework structure ofthe molecular sieve contains less than 1000 ppm Al. Preferably, lessthan 500 ppm Al is present in the framework structure. The Si to Almolar ratio (Si:Al) is advantageously at least 750, more preferably atleast 1000. Most preferably, less than 100 ppm Al is present.

Zeolite beta is characterized by 12-member ring pore openings and athree dimensional interconnecting channel system; its frameworkstructure is more completely described in U.S. Pat. No. 3,308,069,Szostak, Handbook of Molecular Sieves, pp. 92-96, Higgin et al.,Zeolites, 8, 446 (1986), and Treacy et al., Nature, 332, 249 (1988). Thecatalyst utilized in the invention thus has a fundamentally differentstructure than the titanium-containing molecular sieves reported in theprior art (e.g., the TS-1 catalyst described in U.S. Pat. No. 4,410,501,which has an MFI structure; the TS-2 catalyst described by Reddy et al.in Appl. Cat. 58, L1 (1990), which has a ZSM-11 structure).

In preferred embodiments, the titanium-containing molecular sieve hasrelatively large pores (equal to or greater than about 6 angstroms onaverage) and has a zeolite-type structure comprised of Si and a lesseramount of Ti. A crystallinity of greater than 75% is usually desirable.Preferably, the molar ratio of Ti:Si is from 0.1:99.9 to 20:80, withratios in the range of 1:99 to 15:85 being especially preferred. Thetitanium-containing molecular sieve advantageously may have a titaniumcontent of from 1 to 10 weight percent.

The general formula for the titanium-containing molecular sieve ispreferably as follows:

    SiO.sub.2 :yTiO.sub.2

wherein y is from 0.01 to 0.25 (preferably, 0.03 to 0.20).

A suitable method for the preparation of the aforedescribedtitanium-containing molecular sieves involves a procedure whereinzeolite beta is dealuminated and the framework vacancies created bydealumination filled by titanium atoms. This method is preferred for usesince it is relatively rapid and provides high yields of activecatalyst, as compared to, for example, hydrothermal techniques which canrequire 1 week or more per batch and which provide lower yields ofcatalyst. Post-synthesis dealumination methods are well-known andinclude, for example, reaction or leaching with mineral acids (e.g.,HCI, H₂ SO₄, HNO₃) or chelating agents and hydrothermal or steamingtreatments (possibly combined with acid leaching). See, for example, theextensive listing of publications describing zeolite dealuminationmethods catalogued in U.S. Pat. No. 4,576,805 (col. 8, line 62 throughcol. 9, line 27) and Scherzer, "The Preparation and Characterization ofAluminum-Deficient Zeolites", ACS Syrup. Ser. 248, 157-200 (1984). Aparticularly preferred method employs treatment of zeolite beta with amineral acid such as nitric acid (preferably, 2 to 13 M; mostpreferably, concentrated nitric acid) at a temperature of from 25° C. to150° C. for a period of time of from 5 minutes to 24 hours. Othermineral acids and carboxylic acids could alternatively be used, asdescribed, for example, in British Pat. No. 1,061,847, European Pat.Publication No. 488,867, Kraushaar et al., Catalysis Letters 1, 81-84(1988), Chinese Pat. No. 1,059,701 (Chem. Abst. 117:114655g), EuropeanPat. Publication No. 95,304, and Chinese Pat. No. 1,048,835 (Chem. Abst.115:52861 u). The beta zeolite is desirably suspended in or otherwisecontacted with a relatively large volume of the nitric acid (preferably,from 10 to 1000 parts by weight nitric acid per 1 part by weight of thezeolite beta). Multiple dealuminations of this sort may be performed toeffect more complete Al removal. Suitable dealumination methods of thistype are described in more detail in Lami et al., Microporous Materials1, 237-245 (1993), and European Pat. Publication No. 488,867. Thedealuminated material may thereafter be contacted with a titaniumsource. For example, the dealuminated zeolite beta may be exposed to avolatile titanium source such as TiCl₄ vapor in nitrogen for 1 to 24hours at an elevated temperature (preferably, 250° C. to 750° C.). Aliquid phase source of titanium such as (NH₄)₂ TiF₆ (aq.) or TiF₄ (aq.)may alternately be utilized to insert Ti atoms into the frameworkvacancies of the dealuminated zeolite beta. Methods of post-synthesistitanium incorporation into zeolite materials are described, forexample, in U.S. Pat. No. 4,576,805, U.S. Pat. No. 4,828,812, andKraushaar, et al., Catal. Lett. 1, 81-84 (1988). It may be desirable tothen treat the titanium-containing molecular sieve with an ammonium saltsuch as ammonium nitrate, an acid solution (such as aqueous nitric acid)or the like to convert the titanium source to acid form (i.e., hydrogenor hydronium form) or to remove extra-framework aluminum. Water-washing,drying, and/or calcination may also be advantageous.

To further enhance the performance of certain titanium-containingmolecular sieves prepared as described hereinabove, it may beadvantageous to contact the catalyst with an ammonium, alkali metaland/or alkaline earth metal compound. Without wishing to be bound bytheory, it is believed that this enhancement is attributable to theneutralization of certain metal-associated acidic sites present in thetitanium-containing molecular sieve. A preferred method foraccomplishing this modification is to dissolve the ammonium, alkalimetal or alkaline earth metal compound in water or other suitable liquidmedium; the resulting solution is then brought into intimate contactwith the molecular sieve. This procedure preferably is performed at atemperature sufficiently high so as to accomplish the partial (i.e., atleast 25%) or complete exchange or replacement of the ammonium, alkalimetal or alkaline earth metal for the hydrogen cations of the acidicsites within a practicably short period of time (e.g., within 24 hours).For this purpose, temperatures of from about 25° C. to 150° C. willgenerally suffice. The concentration of ammonium, alkali metal oralkaline earth metal compound in the liquid medium may be varied asdesired and will typically be from about 0.001 to 5 molar. Optimumconcentrations may be readily ascertained by routine experimentation.Following the desired cation exchange, the excess liquid medium may beseparated from the modified titanium-containing molecular sieve byfiltration, decantation, centrifugation, or other such technique, andthe modified titanium-containing molecular sieve washed (if desired)with water or other liquid substance, and then dried and/or calcinedprior to use in the epoxidation process of this invention. If anammonium compound has been utilized, calcination is preferably avoidedso as to minimize any re-protonation of the catalyst.

The particular ammonium, alkali metal or alkaline earth metal compoundselected for use is not critical but preferably is water-soluble and isdesirably selected from ammonium, alkali metal or alkaline earth metalhydroxides and oxides (e.g., sodium hydroxide, potassium hydroxide,barium hydroxide, calcium hydroxide), ammonium, alkali metal or alkalineearth metal carbonates (e.g., sodium carbonate, potassium carbonate),ammonium, alkali metal or alkaline earth metal bicarbonates (e.g.,sodium bicarbonate, potassium bicarbonate), ammonium, alkali metal oralkaline earth metal nitrates (e.g., sodium nitrate, potassium nitrate),ammonium, alkali metal or alkaline earth metal halides (e.g., potassiumchloride, sodium bromide, sodium chloride), ammonium, alkali metal oralkaline earth metal sulfates (e.g., sodium sulfate, potassium sulfate),ammonium, alkali metal or alkaline earth metal salts of carboxylic acids(e.g., sodium acetate), and the like and mixtures thereof. The counteranion in the ammonium, alkali metal or alkaline compound should bechosen such that it does not interfere with the desired epoxidationactivity of the modified titanium-containing molecular sieve nordetrimentally alter its crystalline structure. For example, it has beenfound that under certain conditions the use of alkali metalpyrophosphates may deactivate or poison the molecular sieve catalyst.

In one embodiment of the invention, an ammonium, alkali metal, oralkaline earth-modified titanium-containing molecular sieve is generatedin-situ during epoxidation through the use of an unmodifiedtitanium-containing molecular sieve in combination with either anammonium, alkali metal or alkaline earth compound of the type describedpreviously or a buffer comprised of an ammonium, alkali metal oralkaline earth salt of a carboxylic acid or the like. For example, thereaction medium wherein the olefin is contacted with hydrogen peroxidemay contain a NaOAc/HOAc buffer system (preferably, 0.1 to 5M) in asuitable solvent such as an alcohol (e.g., methanol). Alternatively, analkali metal compound alone such as sodium acetate could be utilized. Ina batch process, the ammonium, alkali metal or alkaline earth compoundcould, for example, be added by itself prior to initiation ofepoxidation while in a continuous process (as when a CSTR reactor isemployed) such compound could be combined with one of the feed streamscontaining one of the other reaction components such as the hydrogenperoxide.

The amount of catalyst employed is not critical, but should besufficient so as to substantially accomplish the desired epoxidationreaction in a practicably short period of time. The optimum quantity ofcatalyst will depend upon a number of factors including reactiontemperature, olefin reactivity and concentration, hydrogen peroxideconcentration, type and concentration of organic solvent as well ascatalyst activity. Typically, however, the amount of catalyst will befrom 0.001 to 10 grams per mole of olefin. The concentration of titaniumin the total epoxidation reaction mixture will generally be from about10 to 10,000 ppm.

The catalyst may be utilized in powder, pellet, microspheric,monolithic, extruded, or any other suitable physical form. The use of abinder (co-gel) or support in combination with the titanium-containingmolecular sieve may be advantageous. Supported or bound catalysts may beprepared by the methods known in the art to be effective for zeolitecatalysts in general.

Illustrative binders and supports (which preferably are non-acidic incharacter) include silica, alumina, silica-alumina, silica-titania,silica-thoria, silica-magnesia, silica-zironia, silica-beryllia, andternary compositions of silica with other refractory oxides. Also usefulare clays such as montmorillonites, koalins, bentonites, halloysites,dickites, nacrites, and anaxites. The proportion of titanium-containingmolecular sieve to binder or support may range from 99:1 to 1:99, butpreferably is from 5:95 to 80:20. The catalyst may also be impregnatedor admixed with a noble metal such as Pt, Pd, or the like.

The olefin substrate epoxidized in the process of this invention may beany organic compound having at least one ethylenically unsaturatedfunctional group (i.e., a carbon-carbon double bond) and may be acyclic, branched or straight chain olefin. The olefin may contain arylgroups (e.g,, phenyl, naphthyl). Preferably, the olefin is aliphatic incharacter and contains from 2 to 30 carbon atoms (i.e., a C₂ -C₃₀olefin). The use of light (low-boiling) C₂ to C₁₀ mono-olefins isespecially advantageous. More than one carbon-carbon double bond may bepresent in the olefin; dienes, trienes, and other polyunsaturatedsubstrates thus may be used. The double bond may be in a terminal orinternal position in the olefin or may alternatively form part of acyclic structure (as in cyclohexene, for example). Other examples ofsuitable substrates include unsaturated fatty acids or fatty acidderivatives such as esters or glycerides and oligomeric or polymericunsaturated compounds such as polybutadiene. Benzylic and styrenicolefins may also be epoxidized, although the epoxides of certainstyrenic olefins such as styrene may further react or isomerize underthe conditions utilized in the present invention to form aldehydes andthe like.

The olefin may contain substituents other than hydrocarbon substituentssuch as halide, carboxylic acid, ether, hydroxy, thiol, nitro, cyano,ketone, acyl, ester, anhydride, amino, and the like.

Exemplary olefins suitable for use in the process of this inventioninclude ethylene, propylene, the butenes (e.g., 1,2-butene, 2,3-butene,isobutylene), butadiene, the pentenes, isoprene, 1-hexene, 3-hexene,1-heptene, 1-octene, diisobutylene, 1-nonene, 1-tetradecene,pentamyrcene, camphene, 1-undecene, 1-dodecene, 1-tridecene,1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene,1-nonadecene, 1-eicosene, the trimers and tetramers of propylene,styrene (and other vinyl aromatic substrates), polybutadiene,polyisoprene, cyclopentene, cyclohexene, cycloheptene, cyclooctene,cyclooctadiene, cyclododecene, cyclododecatriene, dicyclopentadiene,methylenecyclopropane, methylenecyclopentane, methylenecyclohexane,vinyl cyclohexane, vinyl cyclohexene, methallyl ketone, allyl chloride,allyl bromide, acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid, crotyl chloride, methallyl chloride, the dichlorobutenes,allyl alcohol, allyl carbonate, allyl acetate, alkyl acrylates andmethacrylates, diallyl maleate, dially phthalate, unsaturatedtriglycerides such as soybean oil, and unsaturated fatty acids, such asoleic acid, linolenic acid, linoleic acid, erucic acid, palmitoleicacid, and ricinoleic acid and their esters (including mono-, di-, andtriglyceride esters) and the like.

Mixtures of olefins may be epoxidized and the resulting mixtures ofepoxides either employed in mixed form or separated into the differentcomponent epoxides.

The process of this invention is especially useful for the epoxidationof C₂ -C₃₀ olefins having the general structure ##STR1## wherein R¹, R²,R³, and R⁴ are the same or different and are selected from the groupconsisting of hydrogen and C₁ -C₂₀ alkyl.

The oxidizing agent employed in the process of this invention is ahydrogen peroxide source such as hydrogen peroxide (H₂ O₂) or a hydrogenperoxide precursor (i.e., a compound which under the epoxidationreaction conditions is capable of generating or liberating hydrogenperoxide).

The amount of hydrogen peroxide relative to the amount of olefin is notcritical, but most suitably the molar ratio of hydrogen peroxide:olefinis from 100:1 to 1:100 when the olefin contains one ethylenicallyunsaturated group. The molar ratio of ethylenically unsaturated groupsin the olefin substrate to hydrogen peroxide is more preferably in therange of from 1:10 to 10:1. One equivalent of hydrogen peroxide istheoretically required to oxidize one equivalent of a mono-unsaturatedolefin substrate, but it may be desirable to employ an excess of onereactant to optimize selectivity to the epoxide. In particular, the useof a small to moderate excess (e.g., 5 to 50%) of olefin relative tohydrogen peroxide may be advantageous for certain substrates.

Although the hydrogen peroxide to be utilized as the oxidizing agent maybe derived from any suitable source, a distinct practical advantage ofthe process of this invention is that the hydrogen peroxide may beobtained by contacting a secondary alcohol such as alpha-methyl benzylalcohol, isopropyl alcohol, 2-butanol, or cyclohexanol with molecularoxygen under conditions effective to form an oxidant mixture comprisedof secondary alcohol and hydrogen peroxide (and/or hydrogen peroxideprecursors). Typically, such an oxidant mixture will also contain aketone such as acetophenone, acetone, or cyclohexanone corresponding tothe secondary alcohol (i.e., having the same carbon skeleton), minoramounts of water, and varying amounts of other active oxygen speciessuch as organic hydroperoxides. Molecular oxygen oxidation ofanthrahydroquinone, alkyl-substituted anthrahydroquinones, orwater-soluble anthrahydroquinone species may also be employed togenerate the hydrogen peroxide oxidant. The hydrogen peroxide may begenerated in situ immediately prior to or simultaneous with epoxidation,as described, for example, in European Pat. Publication No. 526,945,Japanese Kokai No. 4-352771, Ferrini et al., "Catalytic Oxidation ofAlkanes Using Titanium Silicate in the Presence of In-Situ GeneratedHydrogen Peroxide", DGMK Conference on Selective Oxidations inPetrochemistry, Sep. 16-18, 1992, pp. 205-213, and European Pat. Pub.No. 469,662.

If desired, a solvent may additionally be present during the epoxidationprocess of this invention in order to dissolve the reactants other thanthe titanium-containing molecular sieve catalyst, to provide bettertemperature control, or to favorably influence the epoxidation rates andselectivities. The solvent, if present, may comprise from 1 to 99 weightpercent of the total epoxidation reaction mixture and is preferablyselected such that it is a liquid at the epoxidation reactiontemperature. Organic compounds having boiling points at atmosphericpressure of from about 25° C. to 300° C. are generally preferred foruse. Excess olefin may serve as a solvent or diluent. Illustrativeexamples of other suitable solvents include, but are not limited to,ketones (e.g., acetone, methyl ethyl ketone, acetophenone), ethers(e.g., tetrahydrofuran, butyl ether), nitriles (e.g., acetonitrile),aliphatic and aromatic hydrocarbons, halogenated hydrocarbons, andalcohols (e.g., methanol, ethanol, isopropyl alcohol, t-butyl alcohol,alpha-methyl benzyl alcohol, cyclohexanol). An important practicaladvantage of the present invention is that it may readily be practicedusing bulkier alcohol solvents such as alpha-methyl benzyl alcohol,whereas poor results are obtained with such solvents when othertitanium-containing molecular sieves such as TS-1 are utilized ascatalyst. This flexibility minimizes the problems which might otherwisebe encountered when trying to separate the epoxide product from theepoxidation reaction mixture. Quantitative removal of methanol, forexample, from a relatively light epoxide such as propylene oxide isdifficult due to the similarity in their boiling points. More than onetype of solvent may be utilized. Water may also be employed as a solventor diluent; surprisingly, the process of the invention proceeds withminimal hydrolysis even when a significant quantity of water is presentin the epoxidation reaction mixture. Biphasic as well as monophasicreaction systems thus are possible using the present invention.

The reaction temperature is not critical, but should be sufficient toaccomplish substantial conversion of the olefin to epoxide within areasonably short period of time. It is generally advantageous to carryout the reaction to achieve as high a hydrogen peroxide conversion aspossible, preferably at least 50%, more preferably at least 90% mostpreferably at least 95%, consistent with reasonable selectivities. Theoptimum reaction temperature will be influenced by catalyst activity,olefin reactivity, reactant concentrations, and type of solventemployed, among other factors, but typically will be in a range of fromabout 0° C. to 150° C. (more preferably, from about 25° C. to 120° C.).Reaction or residence times of from about 1 minute to 48 hours (moredesirably, from about 10 minutes to 8 hours) will typically beappropriate, depending upon the above-identified variables. Althoughsubatmospheric pressures can be employed, the reaction is preferably(especially when the boiling point of the olefin is below theepoxidation reaction temperature) performed at atmospheric pressure orat elevated pressure (typically, between 1 and 100 atmospheres).Generally, it will be desirable to pressurize the epoxidation vesselsufficiently maintain the reaction components as a liquid phase mixture.Most (i.e., over 50%) of the olefin should preferably be present in theliquid phase.

The process of this invention may be carried out in a batch, continuous,or semi-continuous manner using any appropriate type of reaction vesselor apparatus such as a fixed bed, transport bed, fluidized bed, stirredslurry, or CSTR reactor in a monophase or biphase system. Known methodsfor conducting metal-catalyzed epoxidations of olefins using hydrogenperoxide will generally also be suitable for use in this process. Thus,the reactants may be combined all at once or sequentially. For example,the hydrogen peroxide or hydrogen peroxide precursor may be addedincrementally to the reaction zone. The hydrogen peroxide could also begenerated in situ within the same reactor zone where epoxidation istaking place. Once the epoxidation has been carried out to the desireddegree of conversion, the epoxide product may be separated and recoveredfrom the reaction mixture using any appropriate technique such asfractional distillation, extractive distillation, liquid-liquidextraction, crystallization, or the like. After separating from theepoxidation reaction mixture by any suitable method such as filtration,the recovered catalyst may be economically re-used in subsequentepoxidations. Where the catalyst is deployed in the form of a fixed bed,the epoxidation product withdrawn as a stream from the epoxidation zonewill be essentially catalyst free with the catalyst being retainedwithin the epoxidation zone. In certain embodiments of the instantprocess where the epoxide is being produced on a continuous basis, itmay be desirable to periodically or constantly regenerate all or aportion of the used titanium-containing molecular sieve catalyst inorder to maintain optimum activity and selectivity. Suitableregeneration techniques include, for example, treating the catalyst withsolvent, calcining the catalyst, and/or contacting the catalyst with anammonium, alkali metal or alkaline earth compound. Any unreacted olefinor hydrogen peroxide may be similarly separated and recycled.Alternatively, the unreacted hydrogen peroxide (especially if present atconcentrations too low to permit economic recovery) could be thermallyor chemically decomposed into non-peroxy species such as water andoxygen, for example. In certain embodiments of the process where thehydrogen peroxide is generated by molecular oxygen oxidation of asecondary alcohol, the crude epoxidation reaction mixture will alsocontain a secondary alcohol and a ketone corresponding to the secondaryalcohol. After separation of the epoxide from the secondary alcohol andthe corresponding ketone, the ketone may be converted back to secondaryalcohol by hydrogenation. For example, the ketone may be reacted withhydrogen in the presence of a transition metal hydrogenation catalystsuch as a Raney nickel, copper chromite, ruthenium, or supportedpalladium catalyst. Hydrogenation reactions of this type are well knownto those skilled in the art. The secondary alcohol may also bedehydrated using known methods to yield valuable alkenyl products suchas styrene.

The titanium-containing molecular sieve described herein, in addition tobeing a useful epoxidation catalyst, also has utility as an ionexchanger, a shape-selective separation medium, or a catalyst for otherhydrocarbon conversion processes, including, for example: cracking,selectoforming, hydrogenation, dehydrogenation, oligomerization,alkylation, isomerization, dehydration, hydroxylation of olefins oraromatics, alkane oxidation, reforming, disproportionation, methanation,and the like. The molecular sieve of this invention is particularlyuseful for catalyzing the same reactions wherein titanium silicalites(also referred to as titanium silicates) have heretofore been employed.Illustrative applications of this type are as follows:

a) A process for the manufacture of a ketone oxime which comprisesreacting a ketone such as cyclohexanone with ammonia and hydrogenperoxide in the liquid phase at a temperature of from 25° C. to 150° C.in the presence of a catalytically effective amount of thetitanium-containing molecular sieve. Reactions of this type are wellknown in the art and suitable conditions for carrying out such asynthetic transformation in the presence of a titanium silicalitecatalyst are described, for example, in U.S. Pat. No. 4,745,221, Roffiaet al., "Cyclohexanone Ammoximation: A Breakthrough in the 6-CaprolactamProduction Process", in New Developments in Selective Oxidation, Centiet al, eds., pp. 43-52 (1990), Roffia et al., "A New Process forCyclohexanonoxime", La Chimica and L'Industria 72, pp. 598-603 (1990),U.S. Pat. Nos. 4,894,478, 5,041,652, 4,794,198, Reddy et al.,"Ammoximation of Cyclohexanone Over a Titanium Silicate MolecularSieve", J. Mol. Cat. 69, 383-392 (1991), European Pat. Pub. No. 496,385,European Pat. Pub. No. 384,390, and U.S. Pat. No. 4,968,842, (theteachings of the foregoing publications are incorporated herein byreference in their entirety).

(b) A process for oxidizing a paraffinic compound (i.e., a saturatedhydrocarbon) comprising reacting the paraffinic compound at atemperature of from 25° C. to 200° C. with hydrogen peroxide in thepresence of a catalytically effective amount of the titanium-containingmolecular sieve. Reactions of this type are well known in the art andsuitable conditions for carrying out such a synthetic transformation inthe presence of a titanium silicalite are described, for example, inHuybrechts et al., Nature 345,240 (1990), Clerici, Appl. Catal. 68, 249(1991), and Tatsumi et al., J. Chem. Soc. Chem. Commun. 476 (1990),Huybrechts et al., Catalysis Letters 8, 237-244 (1991 ), the teachingsof which are incorporated herein by reference in their entirety.

(c) A process for hydroxylating an aromatic hydrocarbon (e.g., phenol)comprising reacting the aromatic compound at a temperature of from 50°to 150° C. with hydrogen peroxide in the presence of a catalyticallyeffective amount of the titanium-containing molecular sieve to form aphenolic compound (e.g., cresol). Reactions of this type are well knownin the art and suitable conditions for carrying out such a synthetictransformation in the presence of a titanium silicalite catalyst aredescribed, for example, in U.S. Pat. No. 4,396,783, Romano et al.,"Selective Oxidation with Ti-silicalite", La Chimica L'Industria 72,610-616 (1990), Reddy et al., Applied Catalysis 58, L1-L4 (1990),

(d) A process for isomerizing an aryl-substituted epoxide to thecorresponding beta-phenyl aldehydes comprising contacting thearyl-substituted epoxide with a catalytically effective amount of thetitanium-containing molecular sieve at a temperature of from 25° C. to150° C. See, for example, U.S. Pat. No. 4,495,371 (incorporated hereinby reference in its entirety).

(e) A process for oxidizing a vinyl benzene compound to thecorresponding beta-phenyl aldehyde comprising reacting the vinyl benzenecompound with hydrogen peroxide at a temperature of from 20° C. to 150°C. in the presence of the titanium-containing molecular sieve. See, forexample, U.S. Pat. No. 4,609,765 (incorporated herein by reference inits entirety).

(f) A process for synthesizing an N, N-dialkyl hydroxylamine comprisingreacting the corresponding secondary dialkyl amine with hydrogenperoxide in the presence of the titanium-containing molecular sieve.See, for example, U.S. Pat. No. 4,918,194 (incorporated herein byreference in its entirety).

(g) A process for oxidizing an aliphatic alcohol comprising reacting thealiphatic alcohol with hydrogen peroxide in the presence of thetitanium-containing molecular sieve at a temperature of from 25° C. to150° C. to form the corresponding ketone or aldehyde of said aliphaticalcohol. See, for example, U.S. Pat. No. 4,480,135 (incorporated hereinby reference in its entirety).

(h) A process for synthesizing a glycol monoalkyl ether comprisingreacting an olefin, an aliphatic alcohol, and hydrogen peroxide in thepresence of the titanium-containing molecular sieve at a temperature offrom 25° C. to 150° C. See, for example, U.S. Pat. No. 4,476,327(incorporated herein by reference in its entirety).

From the foregoing description, one skilled in the art can readilyascertain the essential characteristics of this invention, and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages,conditions, and embodiments.

The following examples further illustrate the process of this invention,but are not limitative of the invention in any manner whatsoever.

EXAMPLE 1

This example demonstrates the preparation of a titanium-containingmolecular sieve in accordance with the present invention and its utilityan olefin epoxidation catalyst.

Calcined zeolite beta (5 g; Conteka 41-89-001 ) having a SiO₂ :Al₂ O₃ratio of 24 is added to 500 ml of 13N nitric acid. The resultingsuspension is heated at 80° C. for four hours with stirring. Thesuspended solids are recovered by filtration and retreated twice in thesame manner with fresh portions of 13N nitric acid. After recovering byfiltration, the solids are washed well with deionized water, and driedat 95° C. overnight to provide a dealuminated zeolite beta having aSi/Al molar ratio of 940.

The dealuminated zeolite beta is added to a fitted quartz tube. The tubeis loaded vertically in a furnace and a slow (100 cc/min) nitrogen flowinitiated. The sample is heated at 400° C., then heated at 600° C. andthe nitrogen flow increased to 300 cc/min. Once the temperature hasstabilized at 600° C., the sample is treated with titanium tetrachloridefor eight hours by sparging the nitrogen feed through a warmed (40° C.)TiCl₄ solution. After this time, TiCl₄ treatment is discontinued andnitrogen flow through the sample continued at 600° C. for an additionalhour. The sample is cooled to room temperature overnight with continuousnitrogen flow. The cooled sample is treated with a 1M aqueous solutionof ammonium nitrate at 80° C. for four hours. The sample is recovered byfiltration, washed well with water, dried at 95° C. and then calcined at550° C. for 6 hours to yield a titanium-containing molecular sievehaving a very low level of aluminum. Raman spectroscopy and ²⁹ Si and ²⁷Al MAS NMR also confirmed that near complete dealumination takes placeand that titanium is inserted into the framework of the zeolite. Thex-ray powder diffraction pattern of the titanium-containing molecularsieve is shown in FIG. 1 and summarized in Table II. From ²⁷ Al MAS NMR,it is estimated that less than 100 ppm aluminum is present.

The titanium-continuing molecular sieve thus obtained is evaluated as acatalyst for the hydrogen peroxide epoxidation of 1-hexane using thefollowing conditions: 60° C., 12.2 g methanol (solvent), 16.5 mmol1-hexene, 4.5 mmol hydrogen peroxide, 0.10 g catalyst.

The results of this evaluation are shown in Table I. Example 1-A showsthat good epoxide selectivity can be achieved without modification ofthe catalyst with Group IA or Group IIA cations, due (it is believed) tothe extremely low aluminum content of the catalyst. The activity of thecatalyst was quite high, with over 90% conversion of hydrogen peroxidebeing attained in just one hour. When the catalyst was washed with 0.5%sodium acetate (Example 1-B), a somewhat lower initial rate of hydrogenperoxide reaction was observed together with improved selectivity.Example 1-C demonstrates that the titanium-containing molecular sievewhich has been treated with sodium acetate also performs quitesatisfactorily if alpha-methyl benzyl alcohol rather than methanol isused as a solvent for epoxidation. In contrast, titanium silicalitehaving a TS-1 structure exhibited little activity in an alpha-methylbenzyl alcohol medium (Example 1-D).

                                      TABLE I                                     __________________________________________________________________________                            H.sub.2 O.sub.2        Hexene                                      Catalyst                                                                            Time,                                                                              Conversion                                                                          Epoxide  Glycol Ether                                                                          Conversion,                                                                           Epoxide/Glycol         Example                                                                            Solvent Treatment                                                                           hr   %     Selectivity, %.sup.a                                                                   Selectivity, %.sup.a                                                                  %       Ether                  __________________________________________________________________________                                                           Ratio                  1-A  methanol                                                                              none  1    93    58         1.7   19      3                                         6    96    52       (+17% other)                                                                          31      1                                                             3                                                                             (+39% Other)                           1-B  methanol                                                                              0.5%  1    68    75       5       16      15                                  NaOAc 6    97    63       19      23      4                      1-C  alpha methyl                                                                          0.5%  1    98    68       <2        18.4  >50                         benzyl alcohol                                                                        NaOAc                                                            1-D.sup.c                                                                          alpha methyl                                                                          --(b) 1    no reaction                                                                         --       --      --      --                          benzyl alcohol                                                           __________________________________________________________________________     .sup.a based on hydrogen peroxide                                             (b)TS1 catalyst (U.S. Pat. No. 4,410,501)                                     .sup.c comparative example                                               

                  TABLE II                                                        ______________________________________                                        d(angstroms)  Relative Intensity                                              ______________________________________                                        11.50         vs                                                               6.57         mw                                                               6.05         mw                                                               4.13         w                                                                3.95         s                                                                3.51         mw                                                               3.28         mw                                                               3.24         mw                                                               3,19         w                                                                3.02         w                                                                2.68         w                                                                2.48         w                                                                2.08         w                                                                1.69         w                                                               ______________________________________                                         d = interplanar distance                                                      vs = very strong                                                              s = strong                                                                    mw = medium weak                                                              w = weak                                                                 

We claim:
 1. A process for epoxidation of an olefin comprisingcontacting said olefin with hydrogen peroxide in the presence of acatalytically effective amount of a crystalline titanium-containingmolecular sieve for a time and at a temperature effective to selectivelyform an epoxide of the olefin, wherein the crystallinetitanium-containing molecular sieve is characterized by a frameworkstructure isomorphous to zeolite beta comprised of Si and Ti, butessentially free of framework Al, corresponding to the general formulaSiO₂ :yTiO₂ wherein y is from 0.01 to 0.25.
 2. The process of claim 1wherein the olefin is selected from ethylene, propylene, 1-butene,2-butene, isobutylene, 1-pentene, 2-pentene, cyclopentene, 1-hexene,cyclohexene, vinyl cyclohexane, allyl alcohol, 1-heptene, 1-octene, and1,3-butadiene.
 3. The process of claim 1 wherein the olefin is a C₂ -C₁₀mono-olefin.
 4. The process of claim 1 wherein the temperature is from25° C. to 150° C.
 5. The process of claim 1 wherein the hydrogenperoxide is obtained by molecular oxygen oxidation of a secondaryalcohol.
 6. The process of claim 1 wherein said contacting is carriedout in a liquid phase.
 7. The process of claim 1 wherein from 0.001 to10 grams of the crystalline titanium-containing molecular sieve per moleof olefin is utilized.
 8. A process for epoxidation of a C₂ -C₁₀aliphatic mono-olefin comprising contacting said mono-olefin withhydrogen peroxide in a liquid phase in the presence of from 0.001 to 10grams per mole of mono-olefin of a crystalline titanium-containingmolecular sieve at a temperature of from 25° C. to 120° C. for a timeeffective to selectivity form an epoxide of the mono-olefin, wherein thecrystalline titanium-containing molecular sieve is characterized by aframework structure isomorphous to zeolite beta comprised of Si and Ti,but less than 1000 ppm framework Al, corresponding to the generalformula SiO₂ :yTiO₂ wherein y is from 0.03 to 0.20.
 9. The process ofclaim 8 wherein the mono-olefin is propylene.